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In healthy adults younger than 65 years the effectiveness of influenza vaccination is up to 90% for laboratory confirmed influenza, but is far less in elderly individuals over 65 years and those with comorbidities. However the vaccination in elderly people is effective in preventing complications of influenza infection: pneumonia, hospital admission and death from influenza or pneumonia. This effect is larger for elderly individuals living in nursing homes than in those living in the community. Recommendations at present include vaccination of all people over the age of 65, of high-risk groups, and of those who can transmit influenza to high-risk individuals (healthcare workers). Since 2005 it is recommended that people with occupational contact with wild or domestic birds should be vaccinated to reduce the risk of simultaneous infection with a human and an avian influenza virus. Influenza vaccination is considered to be safe: side effects are reversible within 1-2 days, severe complications are exceedingly rare. Most frequently inactivated vaccines are used, but in the USA there is also an attenuated live vaccine available. They all contain surface antigens of two influenza A strains and one influenza B strain. The world health organization (WHO) selects every year the strains to be included in the vaccine and the viruses are then grown on embryonated chicken eggs. This process requires detailed planning up to 6 months. Because a pandemic event cannot be predicted, this period is too long and there is an urgent need to develop techniques to reduce the vaccine production time and enhance its efficacy. Additionally, several researchers are exploring the possibility of generating a universal vaccine against influenza A virus that does not require reformulation on an annual basis.

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